Well, I have to say at the time I installed it in 2010 it was about the only option that offered the features I needed. Also, I didn't mind paying for the Gold Cart to add even more options. The problems came when I tried to get it working correctly. It did take a bit of battling to get everything working correctly, with some need for a bit of hacking.
There have been improvements made through the years, but still some bugs that never did get fixed (negative tax on discounts), that I still have to work around today. And their original forum doesn't do much to answer problems. In fact most of the help I have received has been from the community that uses the tool. And after all this track record, their premium support asks for WordPress and FTP access to your site (Yikes!), that seem scary to me.
Bottom line, it does almost everything I need it to but it feels like a house of cards waiting to tumble. I just wish it was more stable and problems were identified faster and fixed properly.